Electrical system useful for intrusion alarm with selective sensitivity



Dec. 22, 1964 B. MULVEY ELECTRICAL SYSTEM USEFUL FOR INTRUSION ALARMWITH SELECTIVE SENSITIVITY 2 Sheets-Sheet 1 Filed Oct. 28. 1959 MONITORPOWER SOURCE DAY SWITCH NIGHT ALARM SENSOR FIG.|

INVENTOR.

LOUIS B, MULVEY ATTORN EYS Dec. 22, 1964 I B. MULVEY ELECTRICAL SYSTEMUSEFUL. FOR INTRUS 3,1 62,848 ION ALARM WITH SELECTIVE SENSITIVITY 2Sheets-Sheet 2 Filed 001;. 28, 1959 R S mm W N N E R V 0 M T m MIN s Umdc w fi I I l I I l I I I I I l l I I I :1 I l I I l I I I I I I I I II l I l l I I I I I J United States Patent 3,162,848 ELECTRICAL SYTEMUEFUL ENERUSEON ALARM Wl'il-l SELEiITIVE SENSETIVHY Louis B. lt iulvey,Newt-on, Mass. (19 S. Main St Qohasset, Mass.) Filed 9st. 2%, H59, Ser.No. 849,274

5 Claims. (til. 34tl--25S) The present invention relates in general toelectrical protective systems and more particularly concerns an improved-alarm system having a remote monitor for indicating the presence of anintruder and any deviation from normal operation of the equipment.Either the presence of an intruder or the failure of nearly any elementin the system causes an alarm indication at the monitor. Thus, the novelsystem not only monitors a prescribed surveillance area, but alsoindicates its own malfunctioning.

In a preferred embodiment of the invention, the alarm sensor ispreferably of the type disclosed in a copending application of Louis A.Mulvey, entitled Motion Detector, Serial No. 610,526, filed September18, 1956 now Patent No. 3,126,539. Certain features of the presentinvention represent extensions of the novel concepts disclosed in thatapplication.

In most alarm systems, clever intruders find it possible to enter arestricted area protected by an alarm system without causing an alarmindication. A number of possibilities exist for accomplishing thisresult. For example, it is possible to disable the sensor unit itself insome system without causing an alarm indication. In some remotelymonitored systems, the alarm may be disabled by interfering with thetransmission of signals over the lines coupling the sensor unit in thesurveillance area to the remote monitor.

The present invention contemplates and has as an important object theprovision of an alarm system which is free from the disadvantages notedabove. More particularly, it is an object to provide an electricalprotective system having a sensor coupled to a remote monitor whichindicates an alarm when an intruder interferes with the normal operationof the sensor unit or the lines coupling the sensor to the monitor.

Still another object of the invention is the provision of means forselectively changing the sensitivity of the system in accordance Withthe prevailing conditions then in existence at the surveillance areaWhile alerting an observer of the monitor that such change is beingeffected by authorized personnel.

It is still another object of the invention to provide a system inaccordance with the preceding objects which provides an alarm indicationto signify an abnormality in the system.

A further object of the invention is to achieve the foregoing objectwith equipment capable of being operated by self-contained powersupplies and arranged to consume a minimum amount of power.

Still another object of the invention is to provide an electricprotective system utilizing an oscillator circuit operative in thedesired superregenerative mode immediately upon the application ofoperating power to the circuit.

Still another object of the invention is to provide an electricalprotective system utilizing radiating high frequency energy wherein theprotected area may be confined to a prescribed perimeter invisible to anintruder.

According to the invention, an alarm sensor and associated control meansare located within the surveillance area and conductors couple theseunits to a remote monitor. The signal delivered over each conductor isarranged to pass through a bistable device whose state is reversed inresponse to a prescribed change in potential on the ice associated line.This switching of the bistable device then causes an alarm indication.Thus, anyone cutting the wire or otherwise interfering with thetransmission of a signal thereof causes the monitor to indicate an.alarm condition.

According to another feature of the invention, the sensor comprises asuperregen'erative oscillator. This oscillator receives energizingpotentials from a low impedance power supply through a resistor. Thepresence of this resistor is important because it insures that theoscillator will immediately go into superregeneration when the powerswitch is turned on.

Still another feature of the invention resides in utilizing a wavetransmission conduit having apertures for radiating electromagneticenergy. This is advantageous because the conduits may be routed alongthe perimeter of the surveillance area or buried in the earth and hiddenfrom the View of intruders. An alarm will be sounded whenever an objectapproaches thi perimeter. By guiding the electromagnetic energy in thismanner, sensitivity of the sensor is maximized at the perimeter of thesurveillance area While minimizing spurious responses due to normalactivity within the perirnete Other features, objects and advantages ofthe invention will become apparent from the following specification whenread in connection with the accompanying drawing in which:

FIG. 1 is a block diagram generally illustrating the logical arrangementof the novel electrical protection system;

FIG. 2 is a combined block-schematiccircuit diagram of a preferredembodiment of the invention; and

FIG. 3 is a pictorial representation of the preferred means for guidingthe radiated energy so that sensitivity in the vicinity of the perimeterof the surveillance area is maximized While unwanted spurious responseare minimized.

With reference now to the drawing and more particu larly to FIG. 1thereof, there is illustrated a block diagram generally illustratingthelogical arrangement of a system arranged according to the invention.

The surveillance area it includes an alarm sensor 12 and a day-nightswitch 13. The alarm sensor 12 preferably includes a superregenerativeoscillator. However, the invention contemplates other types ofalarm-indicating devices, whether they do or do not rely uponelectromagnetic radiation in sensing an alarm condition.

The day-night switch 13 includes means for selecting a desired degree ofsensitivity. For example, in the daytime when the area is being watchedmanually, it is generally desired to reduce the sensitivity appreciably.On the other hand, at night it is generally desired to operate thesystem with high sensitivity.

The day-night switch 13 includes a test button for operation in causingthe neon bulb 14 and the selected one of neon bulbs 16 and 117 to flashat the monitor in synchronism in accordance with a prearranged code. Thetest button is manually operated when the sensitivity is changed so thatan operator at the monitor recognizes an authorized witching. A

Two lines, L1 and L2, couple signals from the daynight switch 13 to themonitor 15. Both the day-night switch 13 and the monitor 15 have agrounded terminal. When the day-night switch 13 is set to the dayposition, a potential is delivered on line L2 causing the day bulb in tobe ignited. Under night conditions, a potential is delivered on line L1to ignite the night bulb 17. Any change in potential on the activatedline will cause the warning light 21 to ignite and the buzzer 22 tosound.

The mode of operation of the system will be better understood afterconsidering a preferred embodiment of the invention. Referring to FIG.2, there is shown a 27 in serieswith a resistor 28 having an impedancewhich is high compared to that of the power supply. The

inclusion of the resistor 28 has been discovered to be important becauseit insures that theoscillator will go into superre generation as soon asthe power supply 24- is turned on. If this resistor is omitted,superregeneration may not always occur. The other end of the inductor 27is connected through. an inductive loop coupled to the superregenerativeoscillator tuned circuits 2S? and 3b to antenna 225.

The grid of tube V1 is coupled to the ground bus 31 through a variableresistance 32, the adjustment of this resistance determining the quenchrate of the superregenerative oscillator. A pair of tuned circuits 29and 30 are coupled from the grid to the plate and cathode respectively.These circuits are tuned to the vicinity of the desired radiated carrierfrequency and largely control this frequency.

Capacitor 33 and inductor 34 form a tuned circuit which is normallytuned above the quiescent quench rate so that it functions incooperation with diode D1 as a slope detector. The signal on the plateof tube V1 is connected to the latter slope detector through capacitor38.

Under quiescent conditions, the anode of diode D1' is at a prescribedD.-C. potential so that capacitors 35 and 36 are appropriately charged.Under quiescent conditions, PNP transistor T1 is normally conductivebecause the base is biased slightly negative with respect to the emitterby means of resistor 3'7. Therefore, any change in quench rate,indicative of a change in an object position sensed by the antenna 23,develops a pulse which is applied through capacitor 36 to the base oftransistor T1. The amplified pulse is delivered through load resistor 41to line 42. The utilization of this signal is discaused below inconnection with the description of the monitor.

Considering now the day-night switch 13, it will be seen that line 42 isconnected to line L]. through the arm of test switch 43 and the arm 44of the triple-pole doublethrow day-night switch 45 when this switch isin the night position.

In the night position, a variable resistance as is connected between theanode of diode D1 and the emitter of transistor T1. The value of thisresistance is related to the desired sensitivity for night operation.'By decreasing the resistance 46, sensitivity is reduced. In the dayposition, sensitivity is reduced because the-arm 47 of switch 45connects the potentiometer 48 across the potentiometer 46 to reduce thetotal resistance between the emitter of transistor T1 and the anode ofdiode D1. Then switch 45 is in the day position, the arm 44 connectsline 42 to line L2. v p

Neon bulb 14 is normally extinguished. However, when'the arm of switch43 is depressed, a p tential is applied across bulb 14 to ignite it.Since this is a springloaded switch, an operator may key this switch inaccordance with ,a prearranged code, causing bulb 14 and one of bulbs 16and 17 to flash accordingly. Actuation of switch .43 also providesvisual indication of sensor response to activity in the sensor area bymeans of shunting the sensor signal output current through neon bulb 14.Activity near a properly adjusted sensor will cause neon bulb 14 toflicker. Resistor 49 connected across the contact terminals of switch4-9 acts to defeat attempts to tamper with telephone lines L and L byapplying a keep-alive potential to the telephone line not in currentuse. Thus, shunting or opening circuits of either L or L causes atransient signal which actuates the monitor alarm circuit. Switch 39inactivates switch 43 when the TPDT switch array is set inthe dayposition.

The physical arrangement of the monitor is now described. Tne neon bulbs16 and 17 are coupled to juncdon 52 by a resistor 53. A capacitor 54shunted by a resistor 55 is connected between junction- 52 and'theground bus 5 5. The potential between junction 52 and ground bus 56 isA.-C. coupled to opposed corners of the full-wave diode rectifyingbridge 57 by capacitor 58. The remaining two corners of bridge 57 areconnected between the emitter and base of PNP transistor T2.

Transistor T2 is normally conductive. The bias on the base is selectedfor quiescent conditions by adjusting the variable resistance 51. Abattery 62 is connected in series with a relay coil 63 to delivercollector current to transistor T2. A normally open reset switch ,64 isconnected between the junction of resistors 61 and 65 and the base oftransistor T2. The arm 63 of the monitor relay is normally held over tothe left, as indicated, by collector current flow. A permanentconnection is made between the arm and the left hand contact to .avoidinterrupting the flow of collector current due to mechana ical vibrationof the relay.

The armature of switch 66 is normally positioned as shown. An alarmlight 21 is in series with a resistor 67 between the right hand contact71 opposite the relay switch arm 63 and the battery 62. A buzzer 22 isconnected in series between the switch arm 66 and the same batteryelectrode. Thus, when current flow in the relay coil 63 is interrupted,relay armature 68 moves to the right to illuminate bulb 21 and soundbuzzer 22.

Operation of the monitor circuit is as follows. A transient signaldeveloped on line 42 is coupled over the selected one of lines L1 and L2and applied to the rectifying bridge 57. The bridge alters the biasbetween the emitter and base of transistor T2 to renderthis transis: tornonconductive, thereby interrupting the flow of current through relaycoil 63. The relay switch arm 68 moves to the right to cause an alarmindication.

The function of neon bulbs 16 and 17 is to insure that the system willrespond to all intruders. If these bulbs were not present, it would bepossible to place a potentiometer across the lines L1 and L2 andgradually decrease the resistance between these lines and ground untilthey reach ground potential. This could occur without introducing atransient voltage for rectif cation by the bridge 57 to cutofftransistor T2. Byutilizing the neon bulbs 16 and 17, as soon as theextinguishing potential across the illuminated bulb is reached, there isa sudden change in potential which produces a transient voltagerectified by the bridge 57 and'applied to transistor T2 to cut it offand produce an alarm. I

The bulbs 16 and 17 have another function, that of indicating whetherthe day-night switch 13 is set in the day or night sensitivity position.

The bulbs also indicate that power is being supplied a to the sensorunit and that the telephone and other connecting cables are intact.

Flickering intensity of the bulbs also indicates sensor response toactivity in the sensor area when sensitivity controls 46and/or 48 areproperly adjusted.

The bulbs have another function. An operator at the monitor can observeone of neon bulbs 16 and 17 flashing in accordance with the keying ofswitch 43 to insure that an authorized person ischanging thesensitivity.

Resistors 50 and ,51 shunt neon bulbs 17 and 16 to insure that the glowis extinguished when circuits L or L are in a state of slightconduction. The monitor may be reset by pushing the switch 64 whichcouples a potential to the base of transistor T2 efiective in renderingthis transistor again conductive.

and resistor '70 connected between line L and circuit ground is toprovide means for testing the integrity of the telephone lines and themonitor detection and alarm circuits by arbitrarily shunting a smallportion of the sensor quiescent signal output current flowing throughlines L and L to ground, thereby simulating a transient signal andpresenting it through L to the monitor alarm circuit. Thus properoperation of the telephone line and monitor may be tested at will bypersonnel at central guard station.

It will be observed that the system is essentially r'ailsafe. If thesuperregenerative oscillator becomes inoperative for any reason, atransient signal is developed which causes the alarm to sound.Similarly, this will occur if either transistor T1 or T2 becomesnonconductive. The only place where the fail-safe feature is notprovided is in the monitor where an alarm might not be detected it boththe buzzer and warning lamp became inoperative simultaneously. Thismight be corrected in a number of ways, but is so unlikely that it isprobably unnecessary. For example, a second bulb might be connected inparallel across the first bulb. An aging battery is detectable since thelower voltage would cause the transistor T2 current to drop sufiicientlyto activate the alarm. This is readily accomplished because thetransistor may be selected so that it becomes nonconductive at a voltagewhich is higher than that required to illuminate the bulb and operatethe buzzer. Resistor 5? connected between capacitor 58 and the topjunction of diode bridge 57 Serves to limit current surges flowing inthe A.-C. leg of the bridge to permissible diode operating level.

Referring now to PEG. 3, there is shown a combined block-pictorialdiagram of a preferred means for radiating the electromagnetic energy. AWave transmission conduit, such as the rectangular waveguide 81, isrouted along the perimeter of the surveillance area. Energy is exchangedbetween the wave transmission conduit 81 and the high frequencyoscillator 82 through suitable coupling means 83. The specific couplingmeans may be any of the well-known techniques of coupling high frequencyenergy into a waveguide. For example, it might be introduced through asmall coupling loop. The oscillator 82 may be, for example, essentiallythe oscillator shown in FIG. 2.

The wave transmission conduit is preferably arranged with the radiatingslots such as slots 84 oriented in a plane perpendicular to theorientation of the E vector in the wave transmission conduit.

In the illustrated rectangular Waveguide, the slots appear in the broadwalls of the guide. Best results have been found to occur when the slotsare diagonally oriented as shown. It has also been found to be desirableto have a number of groups of slots. The groups of slots are preferablyspaced about six feet apart along the perimeter when using a highfrequency of about 2000 megacycles. An alternate radiating means mightbe a coaxial cable formed with opening in the outer conductor and havingconductors extending from the inner conductor through the openings.

This means for radiating has a number of advantages. First, theperimeter can be concealed from an intruder. Secondly, the sensitivearea of the detector is confined to a narrow region around the perimeterof the surveillance area. Therefore, those Within and without the areafar from the perimeter do not cause the occurrence of spurious alarms.

There has been described a very sensitive and virtually foolproof alarmsystem capable of monitoring a relatively large area. The novel systememploys relatively inexpensive but reliable standard components in acompact arrangement which consumes relatively small amounts of power. Itis evident that those skilled in the art may now make numerousmodifications of and departures from the specific embodiments describedherein without departing from the inventive concepts. Consequently, theinvention is to be construed as limited only by the spirit and scope ofthe appended claims.

What is claimed is: j

1. An alarm monitoring system comprising, meansfor sensing an alarmcondition in a first location, control means at said first location forselectively determining the sensitivity of said sensing means,monitoring means remote from said first location for providing anindication of an alarm condition, a bistable device at the location ofsaid monitoring means, a conductor inseries with said bistable devicenormally direct coupling a direct potential from said control means tosaid monitoring means to maintain said bistable device in a normalstate, said bistable device assuming an abnormal state upon interruptionof said normal direct potential, and means responsive to a change inthestate of said bistable device from said normal to said abnormal statefor actuating said monitoring means to provide an indication of an alarmcondition, said bistable device being a two terminal gas discharge tubehaving conductive and non-conductive states, a second conductor inseries with a second two terminal gas discharge tube direct couplingsaid control means to said monitoring means, said means responsive tothe change in state of said bistable device also responding to a changein the conductive state of said secondgas discharge tube, said tubesbeing conductive during mutually exclusive time intervals. I

2. An alarm monitoring system comprising, means for sensing an alarmcondition in a first location, control means at said first location forselectively determining the sensitivity of said sensing means,monitoring means remote from said first location for providing anindication of an alarm condition, a bistable device at the location ofsaid monitoring means, a conductor in series with said bistable devicenormally direct coupling a direct potential from said control means tosaid monitoring means to maintain said bistable device in a normalstate, said histable device assuming an abnormal state upon interruptionof said direct potential, and means responsive to a change in the stateof said bistable device from said normal to said abnormal state foractuating said monitoring means to provide an indication of said alarmcondition being sensed and a change in the selection of saidsensitivity, said sensing means comprising in combination, an electricalcircuit including a signal amplifying device having an electrode fordeveloping amplified signals in series with an inductor and furtherincluding circuit elements arranged to support and radiatesuperregenerative oscillations, a low impedance source of directpotential, means including a resistor greater than said low impedancefor coupling said source to said electrode through said inductor, atuned circuit resonant at a frequency near the quench rate of saidsuperregenerative oscillations for developing a signal of said quenchrate whose amplitude is a function of the contemporary quench rate,means including a diode for rectifying the latter signal and developinga control, signal representative of said quench rate, and a controltransistor responsive to said control signal for developing a degree ofconductivity related to said control signal, said transistor being inseries with said conductor for controlling the state of said bistabledevice in accordance with said degree of conductivity.

3. An alarm system comprising, a high frequency oscillatory circuitincluding a signal amplifying device having an electrode for developingamplified signals in series with an inductor and further includingcircuit elements arranged to support and radiate superregenerativeoscillations, a low impedance source of direct potential, meansincluding a resistance greater than said low impedance for coupling saidsource to said electrode through said inductor, a wave transmissionconduit formed with radiating apertures therein and positioned along theboundary frequency energy between said circuit and said conduit, .atuned circuit resonant at a frequency nearer the quench rate of saidsuperregenerative oscillations for developing a signal of said quenchrate whose amplitude is a function of the contemporary quenchrate,'means includ-' ing a diode for rectifying the latter signal anddeveloping a control signal representative of said quench rate, a Y

control transistor responsive to said control signal for developing adegreeof conductivity related to said control signal and providing adeviation signal corresponding to said degree of conductivity, controlmeans near the location of said oscillatory circuit responsive to saiddeviation signal exceeding a preselected value to provide an alarmsignal, switching means for selecting one of two magniconductorsrespectively and coupling said conductors to a capacitor in series witha rectifying circuit, the conductive state of that one of said bulbsassociated with the conductor selected by said switching means beingresponsive to said alarm signal, a signal amplifying device normallydelivering energy to alarm indicating means to prevent the latter fromindicating an alarm, said signal amplifying device having a controlelectrode coupled to the output of said rectifying circuit, saidrectifying circuit responding to changes in the conductive state of saidgas discharge bulbs by delivering signals of the proper polarity to'saidcontrol electrode to interrupt the delivery of energy to said alarmindicating means and cause the latter to indicate an alarm, said firstand second conduce tors each normally carrying a direct potentialfromsaid control means to said first and second gas discharge bulbs tomaintain said bulbs normally in the ignited state.

4. An alarm monitoring system comprising,

means for sensing an alarm condition in a first location,

control means at said first location for selectively determining thesensitivity'of said sensing means,

monitoring means remote from said first location for providing anindication of an alarm condition,

a bistable device at the location of said monitoring a conductor inseries with said bistable device normally direct coupling a directpotential from said control means to said monitoring means to maintainsaid bistable device in a normal state,

said bistable device assuming an abnormal state upon interruption ofsaid direct potential,

means responsive to a change in the state of said histable device fromsaid normal state to said abnormal state for actuating said monitoringmeans to provide an indication of said alarm condition being sensed anda change in the selection of said sensitivity,

said means for selectively determining sensitivity com- 8 prisingswitching means for selecting one of a plurality of degrees ofsensitivity, and a conductor and bistable device for each of saiddegrees of sensitivity coupling said control means to said monitoringmeans, each of the latter coupling arrangements delivering signals'to acommon device responsive to a change in the state of any of saidbistable devices to indicate an alarm condition. 5. An alarm monitoringsystem comprising, means for sensing an alarm condition in a firstlocation, controlmeans at said first location for selectivelydetermining the sensitivity of said sensing means, monitoring meansremote from said first IOQatiOn for providing an indication of an alarmcondition, a bistable device at the location of said monitoring means, 7a conductor in series with said bistable device normally direct couplinga direct potential from said control means to said monitoring means tomaintain said bistable device in a normal state, said bistable deviceassuming an abnormal state upon interruption of said direct potential,means responsive to a change in the state of said bistable device fromsaid normal state totsaid abnormal state for actuating said monitoringmeans to provide an indication of said alarm conditioning being sensedand a change in the selection of said sensitivity, said responsive meansat said first remote location comprising ,a signal amplifying devicenormaly delivering energy to alarm indicating means to prevent thelatter from indicating an alarm, said signal amplifying device having acontrol electrode, and arectifying circuit coupling said bistable deviceto said signal amplifying device, I said rectifying circuit respondingto changes in the state of said bistable device by delivering signals ofthe proper polarity to said control electrode .to interrupt delivery ofenergy to said alarm indicating means and cause the latter to indicatean alarm.

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1. AN ALARM MONITORING SYSTEM COMPRISING, MEANS FOR SENSING AN ALARMCONDITION IN A FIRST LOCATION, CONTROL MEANS AT SAID FIRST LOCATION FORSELECTIVELY DETERMINING THE SENSITIVITY OF SAID SENSING MEANS,MONITORING MEANS REMOTE FROM SAID FRIST LOCATION FOR PROVIDING ANINDICATION OF AN ALARM CONDITION, A BISTABLE DEVICE AT THE LOCATION OFSAID MONITORING MEANS, A CONDUCTOR IN SERIES WITH SAID BISTABLE DEVICENORMALLY DIRECT COUPLING A DIRECT POTENTIAL FROM SAID CONTROL MEANS TOSAID MONITORING MEANS TO MAINTAIN SAID BISTABLE DEVICE IN A NORMALSTATE, SAID BISTABLE DEVICE ASSUMING AN ABNORMAL STATE UPON INTERRUPTIONOF SAID NORMAL DIRECT POTENTIAL, AND MEANS RESPONSIVE TO A CHANGE IN THESTATE OF SAID BISTABLE DEVICE FROM SAID NORMAL TO SAID ABNORMAL STATEFOR ACTUATING SAID MONITORING MEANS TO PROVIDE AN INDICATION OF AN ALARMCONDITION, SAID BISTABLE DEVICE BEING A TWO TERMINAL GAS DISCHARGE TUBEHAVING CONDUCTIVE AND NON-CON-